CELL STRUCTURES

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CELL STRUCTURES

• Sources
• Campbell, N. 1993 Biology Third Edition.
  Benjamin Cummings Publishing. United States.
• Wallace, S. 1993 Biology

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The Cytoskeleton

• The cytoskeleton (high voltage transmission
  electron microscope)
• Microfilaments (very fine 6 nm in diameter).
  mostly made up of protein actin. Have a variety
  of roles depending on the type of proteins they
  are associated with
• one is to provide support to the plasma membrane
• form supportive network of microvilli (intestinal
  wall)
• also involved in the pinching of the cell
  membrane during cell division

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• Intermediate filaments (diameter 7 nm) Role is
  poorly understood.
• Found in epithelial cells, nerve cells, muscle
  cell fibers and blood cells.
• Made up of the protein keratin.
• Microtubules (diameter 22 nm)
• Formed from the globular protein tubulin
• form cilia, flagella, centrioles, basal bodies
• Important in cell division where they take a
  spindle form.

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The Endoplasmic Reticulum (ER)

• Endoplasmic inside the cytoplasm
  Reticulum network
• Function
• Plays a role in the cells synthetic ability
  newly synthesized proteins, lipids and
  carbohydrates are transported within the
  endoplasmic reticulums lumen.

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The ER ...

• Structure
• The ER consists of membranous tubules and sacs
  called cisternae. Membranes separate the cytosol
  from the internal compartment of the lumen
• Have the same phospholipid bilayer seen in the
  plasma membrane
• The ER membrane is continuous with the outer of
  the two membranes of the nuclear envelope

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• The Rough Endoplasmic reticulum (RER)
• Occurs in cells that manufacture proteins for
  secretion outside of the cell (i.e digestive
  enzymes and hormones)
• The Smooth Endoplasmic reticulum (SER)
• Abounds in cells that synthesize secrete, and
  store carbohydrates, steroids, lipids and other
  non-protein products.
• Found in testis cells oil glands some hormone
  producing gland cells intestinal cells, where
  they collect products of lipid digestion in
  liver cells the SER is associated with glycogen,
  the animal storage carbohydrate (starch).

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Ribosomes

• Structure Large molecular structures consisting
  of ribosomal rRNA sub-units and proteins.
• Consists of 2 sub-units (large and small) which
  join together to form a functional ribosome only
  when they attach to mRNA
• Ribosomes are constructed in the nucleolus from
  RNA
• Are too large to be considered molecules. The
  ribsomal sub-units in prokaryotes are smaller and
  differ chemically.

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Ribosomes...

• Function Where the cell assembles proteins
  following genetic (DNA) instructions. Ribosomes
  translate message from mRNA
• There are two forms
• Polyribosomes or polysomes Free
• Bound ribosomes Attached to the ER

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The Golgi Apparatus

• Sometimes called Dyctiosomes in plant cells
• Structure (see diagram)
• Component of the endomembrane system
• Made up of flattened bag-like sacs called
  cisternae. Found near the nucleus. (cis phase
  forming face trans face maturing phase)
• Function
• Manufacturing, warehousing, sorting, and shipping
  center of materials in the cell

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Mitochondria

• Structure (see diagram)
• Have double membranes
• Have their own circular DNA and ribosomes (make
  their own proteins)
• Smaller than chloroplasts
• develop from pre-existing mitochondria

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Mitochondria...

• Function
• ATP (adenosine tri-phosphate) generating molecules

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Peroxisomes (Microbodies)

• Structure
• Sacs bound by a single membrane
• Function (see transparency)
• organelles found in nearly all eukaryotic cells
  that contain specialized enzymes for specific
  metabolic activities
• All contain peroxide-producing oxidases (enzymes)
  that transfer H from various substrates to O
  producing H2O2